https://etd.iisc.ac.in/handle/2005/37 Mon, 06 Apr 2026 03:01:43 GMT 2026-04-06T03:01:43Z http://etd.iisc.ac.in:80/bitstream/id/7dc28c4c-7ad5-4a90-a40a-0ed5a4355e84/ https://etd.iisc.ac.in/handle/2005/37 https://etd.iisc.ac.in/handle/2005/5345 Acquiring diagnostic knowledge from documents to predict issues in aircraft assembly Madhusudanan, N Expert knowledge is important in a product's lifecycle, especially during the manufacturing part of the lifecycle. Most of such knowledge is obtained through experience and its reuse can help prevent potential issues in subsequent product development. Extracting the knowledge acquired during one development cycle for reuse in subsequent development closes the knowledge loop within a product's lifecycle. This thesis is aimed at acquiring expert knowledge from the manufacturing and assembly phases in aerospace manufacturing for eventual use in the planning and design stages. Given the difficulties in knowledge acquisition from experts, this thesis focuses on acquiring expert knowledge from text documents. The proposed method consists of three parts - segregation of relevant text, acquisition of issues, causes and parameters, and realising context of knowledge. These parts become the research questions to be addressed in this thesis. The segregation of relevant text involves identifying coherent segments and then classifying the relevant segments. The method proposed for segregation is based on discourse representation that treats documents as a discourse, and attempts to measure topic changes by looking at the relatedness between the discourse entities. A measure for calculating similarity between sentences is used for identifying segments. Implementation and validation of the method with human subjects is described. The acquisition of diagnostic knowledge is performed by first identifying the parts of text containing issues. Functional modelling and sentiment analysis are considered, and the latter is chosen. A strategy for finding the causes of issues based on text patterns and sentiment is proposed. Once the issues and causes are known, the relations and parameters that form the cause are dissected to represent the knowledge as rules in a knowledge base. A hybrid method using both text patterns and dependency parse of the text representing cause is proposed. The knowledge acquisition pipeline from the issues and causes to the rules is implemented. The acquisition of causes and effects is also cross-validated with human subjects. Once the knowledge is acquired, methods for capturing the context (in which it was acquired or it needs to be applied) are proposed. Context containers that make use of proximity of words to ve factors defined to influence assemblability are used to capture the context. It is expected that assembly situations can be described using these, and enable to match the knowledge to a similar situation when reusing the knowledge. At the application stage, an assembly situation model is proposed that combines product and process information to model the application situation. The application of knowledge and implementation of these models is part of a legacy-knowledge based smart manufacturing system under development. This thesis concludes with a discussion of how the objectives were met, how the current methods could be improved and the directions in which the methods could be extended. https://etd.iisc.ac.in/handle/2005/5345 https://etd.iisc.ac.in/handle/2005/603 Advanced Methodologies For Designing Metallic Armour Plates For Ballistic Impact Raguraman, M A Primary objective of the present research is the development of robust CAE (Computer-Aided Engineering)-based approaches for designing armour plates subjected to ballistic impact by small-calibre hardened peojectiles with or without a protective sheath. Amongst the challenges in simulation is the capturing of target plate material behaviour at high strain rates with possibilities of adiabatic heating. A comprehensive numerical study carried out has resulted in the identification of simulation guidelines using a commercially available explicit finite element anlaysis solver (viz. LS_DYNA). The interferences thus drawn in terms of modeling approach 9I.e. shell, solid or axisymmetric or a mixed representation). Mesh density and element type, contact condition, and constitutive model 9I.e. discrete strain-rate based, Cowper-Symonds, or Johnson-Cook) with failure criteria are verifiable and greatly beneficial for armour plate design. Confidence in the suggested procedures has been obtained through extensive correlation of numerical results with experimental residual velocities and ballistic limits as well as projectile and target plate failure modes. A wide range of impact velocities has been considered (from a low velocity of about 5m/s to an ordnance range velocity of 800+ m/s). Target plates made of variants of mild steel and aluminium alloys have been studied. The simulation approaches have been applied to single-layered as well as multi-layered target plates. Although a majority of the comparisons has been made against published test results, a new ballistic impact testing facility has been set up in course of the current research and excellent correlation of numerically predicted residual velocities and failure modes has been obtained against the tests carried out for aluminium plate using the latter facility. A unique feature of the current experimental effort is the capturing of the complete trajectory of projectile beginning with oblique impact through subsequent perforation/ricochet. Furthermore, projectiles of various nose-shapes such as ogival, conical, hemispherical and blunt have been employed. The power of simulation has been demonstrated with the help of a number of parametric studies with variables such as plate thickness and material properties, as well as projectile mass and diameter, and obtaining physically consistent results. Additionally, existing semi empirical models for residual velocity and ballistic limit prediction have been reviewed, and new user-friendly models have been proposed based on energy conservation and predominant shear plugging failure mode of target plate. Finally, the goal of applying the present research work as a design tool can be well-served by packaging the knowledge gathered here in the form of a user-friendly guide with a graphical user interface(GUI). To this end, an application using MS windows VC++ utilities has been created with the functionalities of: (a) viewing reference LS-DYNA input data files for selecting typical problems of impact on steel and aluminium plates; (b) computing complete lists of strain rate-based material quantities required in LS-DYNA material models like discrete strain rate-based, Cowper-Symonds and Johnson-Cook by specifying the minimum number of easily available quasi-static properties (such as elastic modulus, yield and ultimate strengths, etc.), and (c) estimating residual velocities using the semi-empirical relations for steel and aluminium plates derived in the current work. Wed, 02 Sep 2009 09:56:08 GMT https://etd.iisc.ac.in/handle/2005/603 2009-09-02T09:56:08Z https://etd.iisc.ac.in/handle/2005/3751 Advanced Numerical Approaches for Analysis of Vehicle Ride Comfort, Wheel Bearings and Steering Control Mahala, Manoj Kumar Suspension systems and wheels play a critical role in vehicle dynamics performance of a car in areas such as ride comfort and handling. Lumped parameter models (LPMs) are commonly used for assessing the performance of vehicle suspension systems. However, there is a lack of clarity with regard to the relative capabilities of different LPM configurations. A comprehensive comparative study of three most commonly used LPMs of increasing complexity has been carried out in the current work. The study reported here has yielded insights into the capabilities of the considered LPMs in predicting response time histories which may be used for assessing ride comfort. A shortcoming of available suspension system models appears to be in representation of harsh situations such as jounce movement which cause full compression of springs leading to ‘jerks’ manifested as high values of rate of change of acceleration of sprung mass riding on a wheel. In the current research work, a modified nonlinear quarter-car model is proposed to account for the contact force that results in jerk-type response. The numerical solution algorithm is validated through the simulation of an impact test on a car McPherson strut in a Drop Weight Impact Testing Tower developed in CAR Laboratory, CPDM. This is followed by a detailed comparison of HCM and QCM to examine their suitability for such analysis. For decades, wheel bearings in vehicles have been designed using simplified analytical approaches based on Hertz contact theory and test data. In the present work, a hybrid approach has been developed for assessing the load bearing capacity of a wheel ball bearing set. According to this approach, the amplitude of dynamic wheel load can be obtained from a lumped parameter analysis of a suspension system, which can then be used for detailed static finite element analysis of a wheel bearing system. The finite element modelling approach has been validated by successfully predicting the load bearing capacity of an SKF ball bearing set for an acceptable fatigue life. For the first time, using a powerful commercial explicit finite element analysis tool, a detailed dynamic analysis has been carried of a deep groove ball bearing with a rotating inner race. The analysis has led to a consistent representation of complex motions consisting of rotations and revolutions of rolling elements, and generated insights into the stresses developed in the various components such as balls and races. In conclusion, a simple yet effective fuzzy logic-based yaw control algorithm has been presented in the current research. According to this algorithm, two inputs i.e. a yaw rate error and a driver steering angle are used for generating an output in the form of an additive steering angle which potentially can aid a driver in avoiding straying from an intended path. Sat, 23 Jun 2018 00:00:00 GMT https://etd.iisc.ac.in/handle/2005/3751 2018-06-23T00:00:00Z https://etd.iisc.ac.in/handle/2005/1998 Advanced Simulation Methodologies For Crashworthiness And Occupant Safety Assessment Of An Indian Railways Passenger Coach Prabhune, Prajakta Vinayak Accidents involving passenger trains happen regularly in India. The reasons for such accidents could be many; such as weather and flooding, faulty tracks, bridge collapse, collisions caused by signaling errors, mechanical failures, driver error, sabotage etc. The annual accident-related deaths as a percentage of the total number of passengers carried by Indian Railway may seem to be negligible, but the aim should be to achieve zero fatality as every single person killed is an irreplaceable loss to his/her family. It needs to be mentioned that in addition to fatalities for which exact numbers are not available, serious injuries and permanent disabilities caused by train accidents in India at present stand completely unaccounted for. In the absence of a large scale renovation and crash avoidance measures coupled with the propensity to increase the number of trains every year, enhancing passive safety is crucial i.e. crashworthiness and occupant safety of passenger coaches of Indian trains. In the current work, crashworthiness and occupant safety of the existing typical three-tier cabin passenger coach of Indian Railway in an event of collision accident are assessed with the aid of a finite element analysis. In the light of the published work on research in railroad equipment crashworthiness, the current work is intended to envisage the methodology to assess the Indian Railway passenger coach from the point of view of the crashworthiness and occupant safety using CAE (Computer aided engineering) based approach. It is involved with an extensive study of the structural crush behavior of an individual passenger coach car and its effect on the interaction between occupants and the coach interior. Here the structural crush behavior of a typical three-tier cabin passenger coach is evaluated for the head-on impact against a fixed and rigid barrier. The occupant response for the same scenario is also studied which can be viewed as a component of the actual occupant response due to the structural crush behavior of the passenger coach. This can give useful estimates of injury severity and fatalities that may occur in actual accidents. An FE model of the passenger coach structure was built and validated using International Railway Union (UIC) specified code OR 567-design requirements in terms of static loads constituting structural proof cases. These proof cases specify the static load values the coach body structure should withstand without any permanent deformation or failure when applied at the specified locations on the structural ends across the longitudinal axis. In addition, a favorable correlation between the simulation and actual experiment for drop impact behavior of the open section specimens, namely C-section and I-section, was obtained to validate the simulation methodology. LS-DYNA a nonlinear dynamic explicit FE solver was used to carry out all the dynamic impact simulations involved in the current work. The material modeling takes into account the strain rate effect which is essential for the material impact behavior study. The contact modeling was done using penalty contact method. The degrading effect of the buffer on the structural crush patterns which induced the undesirable global bending and jackknifing of the whole coach structure was demonstrated with the help of dynamic impact simulations of the coach structure. The quantification of occupant injury was done by occupant safety simulations using the Hybrid III 50th percentile male dummy FE model. The dummy having been designed for simulating automobile accident scenarios, its contacts had to be adapted to suit the excessive mobility conditions in the coach interior. The dummy was revalidated successfully for the head drop test, pendulum chest impact test, neck flexion and extension test and knee impact test. Impact simulations for three different speeds were performed by positioning the dummy close to the impact point. Injury criteria such as Head Injury Criterion, Chest Deceleration, Knee force level and Neck extension-flexion moments were used to estimate the injury severity level and fatality rate. Tue, 21 May 2013 00:00:00 GMT https://etd.iisc.ac.in/handle/2005/1998 2013-05-21T00:00:00Z